1. Field of Invention
The present invention relates to improved, compact image viewing apparatus and more particularly to viewing apparatus utilizing an active display surface to facilitate compactness.
2. Background of Invention
One limiting factor on the presently expanding growth of micro-information systems, e.g., those using microfilm or microfiche, is the need for improved and more compact magnifying viewers for displaying the information. At present, viewer designs are usually developed: (1) using expensive, large f-number, highly corrected lenses to obtain a shorter projection distance and thus more compact viewers; (2) using less expensive lenses, longer projection distances, and thus less compactness in the overall viewer configuration; or (3) using a compromise between these approaches. An excellent discussion of the problems involved in designing a compact micro-information viewer is set forth in U.S. Pat. No. 3,704,068.
The alternative approach disclosed in U.S. Pat. No. 3,704,068 is to provide a large number of lenslets each adequate to project the image of a small portion of a document, e.g., a single letter, over a very short projection distance. Although this approach has advantages, difficulties can be encountered in apparatus using the approach. For example, special information recording techniques are required for media using such viewers; thus the viewers would not be adaptable to media recorded in present microform formats. Also, optical alignment problems could adversely affect the cost or image quality of the apparatus. Further, the accuracy of optical alignment required during image retrieval can render image selection, from a microform file, difficult.
With regard to certain aspects of the information display technology, other than achieving compactness, the desirability of active display screens has been recognized. Cross-referenced, copending U.S. applications Ser. Nos. 682,304 and 682,305 disclose such active display screens and explain their utility as image intensifiers and as image storers, which facilitate the retrieval of images and conserve usage of the projection source.
Heretofore, however, it has not been recognized that active display screens can be utilized in improving the compactness of viewers.